Topology, Geometry, and Group Theory

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9803374 Davis About 50 years ago, Aleksandrov, Busemann and Wald introduced the idea of defining upper and lower bounds for the ``curvature'' of more general metric spaces than Riemannian manifolds. Aleksandrov was interested primarily in the case of nonnegative curvature and its applications to convex polyhedral surfaces in Euclidean 3-space. Interest in this subject was renewed about ten years ago when Gromov pointed out that for topological and group theoretic reasons the nonpositively curved case was much more interesting than the positively curved case, the main reason being that the universal cover of a nonpositively curved space is contractible. Gromov also pointed out that there were many polyhedral examples of such spaces. In particular, Tits buildings are such examples. For the past several years, Professors Charney and Davis have collaborated in investigating nonpositively curved polyhedra and applications to group theory. The groups in which they are primarily interested are Coxeter groups and Artin groups. Both types of groups are associated to groups generated by reflections. Both Charney and Davis have also accomplished separate research in these areas. They will continue their research on these areas as well as on closely related topics such as the properties of Tits buildings and their automorphism groups. Groups generated by reflections occur in many places in mathematics and in nature (for example, in crystallogrophy). The symmetry groups of regular tilings of the Euclidean plane are such groups. Escher's drawings show examples of regular tilings in non-Euclidean plane geometry. These are also associated with reflection groups. Professors Charney and Davis are interested in such examples in a more abstract setting. It turns out that abstract reflection groups (Coxeter groups) can always be realized as the symmetry groups of a space that is nonpositively curved, much as in the case of the Euclidean and non-Euclidean planes. ***